1. Field of the Invention:
The invention relates to a method and apparatus for measuring gas flow speed by direct pressure measurement and finds particular application as a wind speed threshold detecting means.
There is a need for the development of surface sensors for use in preventing wind-shear related accidents particularly at airports and it is for this application that the development of a gas speed measuring means in accordance with the present invention is particularly, though not exclusively, directed. In this respect, there is a need for surface sensors of high reliability that can be obtained at reasonable cost for use in large numbers. Further, it is desirable to employ wind speed detectors which will in the ideal, measure wind speed irrespective of its direction and which will be relatively insensitive to tilt or wind angle. Thus, the present invention is directed primarily to the provision of apparatus which is concerned with the measurement of gas flow speed alone rather than its direction of flow and which is substantially insensitive to tilt.
Alternative applications for measuring apparatus in accordance with the invention include, for example, the detection of thunderstorm gust fronts, down-slope wind studies, wind caution signs for roads and bridges as well as wind machine protection and site surveys.
2. Prior Art:
It is a conventional expedient when measuring gas flow velocity, to measure the flow pressure by employing pressure measuring probes in the form of pitot/static tubes. In such arrangements, the tubes are generally aligned to sense the pressures associated with a gas stream flowing in a certain direction relative to the tube entrances and such devices have little sensitivity to variations in flow speed in other directions. This is acceptable in many pitot tube applications when measurement of substantially unidirectional streams is required, for example in aircraft where air speed or head wind or tail wind speed is measured.
Devices have, however, been proposed having sensitivity to changes in direction as well as speed of a gas stream. For example, U.S. Pat. No. 2,789,433 to Goudy, Issued Apr. 23, 1957, specifically discloses apparatus for measuring wind speed and direction and employs a substantially flat disc-like pitot head incorporating a number of pitot tubes, the entrances to which are spaced around the periphery of the head whereby each individual tube is particularly sensitive to gas flow in a particular direction. Opposed pairs of the tubes are grouped together to influence separate pressure transducers in the form of diaphragm switches and the outputs of the transducers are used to activate a comparison circuit, which dependent on the transducer outputs produces a field directly representative of the wind direction and strength. The device is relatively complex in its nature, however, and since the pitot tube inlets, which are the only source of pressure signals, are all spaced around the periphery of the disc-like head, would have little sensitivity to wind flowing in planes other than those generally parallel to the plane of the disc.